2008 7th International Pipeline Conference, Volume 3, 2008
When a crack initiates and propagates in a pressurized pipe, the only thing that might stop this ... more When a crack initiates and propagates in a pressurized pipe, the only thing that might stop this high-velocity event is the release of internal pressure (decompression), resulting in a deceleration in the crack-propagation rate. This deceleration can be achieved through the use of crack ...
2010 8th International Pipeline Conference, Volume 2, 2010
ABSTRACT Two types of specimen for crack tip opening angle (CTOA) measurement have been investiga... more ABSTRACT Two types of specimen for crack tip opening angle (CTOA) measurement have been investigated for pipeline applications, i.e., the modified double cantilever beam (MDCB) (at NIST) and the drop-weight tear test (DWTT) specimen (at CANMET). Results of effects of specimen types, thicknesses and loading rates on CTOA are summarized and discussed. The main observations include: (i) For both MDCB and DWTT specimens tested at quasi-static loading rate, crack front tunnelling (i.e., with a deep triangular crack-tip shape) was present in high-strength steels; (ii) For DWTT specimens, CTOA values measured optically at the surface were significantly higher than those from the simplified single-specimen method (S-SSM) and those measured at mid-thickness [on sections cut using electric discharge machining (EDM)]; and (iii) CTOA values from surface measurement of MDCB specimens were comparable to those derived from S-SSM of DWTT specimens, but the surface values of DWTT were higher than those of MDCB specimens.
2008 7th International Pipeline Conference, Volume 3, 2008
ABSTRACT The toughness and plasticity of steel generally decreases with increasing testing rate. ... more ABSTRACT The toughness and plasticity of steel generally decreases with increasing testing rate. The crack tip opening angle (CTOA) was measured on two types of commercial pipeline steels API-X65 and API-X100, at a range of displacement rates to characterize rate effects. The testing was conducted at quasi-static and dynamic rates. The crosshead displacements in our test matrix ranged from 0.002 mm/s in the quasi-static mode to approximately 8000 mm/s in the dynamic mode. The quasi-static tests were conducted in a servo-hydraulic uniaxial test machine using Modified Double Cantilever Beam (MDCB) specimens. The dynamic experiments were made on a similar servo-hydraulic uniaxial test machine using the same type of specimen and with the addition of a disc spring setup for the fastest rate. The results of these tests indicate that the rate effect has negligible influence on the CTOA values measured for these materials for the reported rates. The CTOA values measured for the two materials show a small but convincing difference. The resistance to fracture was found to be higher for the X65 steel, as indicated by a higher CTOA and lower crack growth velocity. This paper presents results on the influence of displacement rates from quasi-static to dynamic for the X65 and X100 grade pipeline steels, and discusses a method for optimizing the reduction of the CTOA data.
A system is described based on electromagnetic acoustic transducers (EMATs) as an approach to aut... more A system is described based on electromagnetic acoustic transducers (EMATs) as an approach to automated nondestructive evaluation of thick weldments. Applications include a new type of ultrasonic inspection system for thick, butt welds used in ship construction. A minicomputer controlled transducer positioned and acquired the digitized ultrasonic waveforms for synthetic aperture processing. The synthetic aperture technique further improved signal quality and yielded flaw localization through the weld thickness. Details include the design of the transducers and electronics, as well as the mechanical positioner, signal processing algorithms, and complete computer program listings.
ABSTRACT The assessment of hydrogen content in pipeline steel is an essential requirement to moni... more ABSTRACT The assessment of hydrogen content in pipeline steel is an essential requirement to monitor loss of pipe integrity with time and to prevent failures. The use of pipeline steels of increasing strength significantly reduces the threshold hydrogen concentration for hydrogen cracking. Cathodic protection and corrosion processes both contribute to accumulation of hydrogen as a function of time, which may eventually meet the cracking criteria. New and unique methodologies based on electronic property measurements offer the pipeline industry advanced non-destructive tools to provide quantified in-situ hydrogen content measurements in real-time. The use of low frequency impedance measurements as a non-contact sensor has been demonstrated for real-time determination of hydrogen content in coated pipeline steel specimens in the laboratory. Scale-up to field measurements is in progress, and the development and use of a field sensor are discussed.
ABSTRACT A measurement system has been developed to investigate the technology required for high-... more ABSTRACT A measurement system has been developed to investigate the technology required for high-power gas-coupled ultrasonics and the phenomenology of finite-amplitude of ultrasonic waves in gases at high frequencies (>10 MHz) and pressures up to 10 MPa (100 bar). Results of measurements of compression wave absorption and velocity in argon between 10 and 25 MHz, with various combinations of pressure, temperature and power level are presented. For small-amplitude waves, the resulting data are in good agreement with those calculated using ideal gas equations and fundamental thermophysical gas constants. At higher power levels, nonlinear phenomena are observed
An insulation system for ITER Central Solenoid must have sufficiently high electrical and structu... more An insulation system for ITER Central Solenoid must have sufficiently high electrical and structural strength. Design efforts to bring stresses in the turn and layer insulation within allowables failed. It turned out to be impossible to eliminate high local tensile stresses in the winding pack. When high local stresses can not be designed out, the qualification procedure requires verification of the acceptable structural and electrical strength by testing. We built two 4×4 arrays of the conductor jacket with two options of the CS insulation and subjected the arrays to 1.2 million compressive cycles at 60 MPa and at 76 K. Such conditions simulated stresses in the CS insulation. We performed voltage withstand tests and after end of cycling we measured the breakdown voltages between in the arrays. After that we dissectioned the arrays and studied micro cracks in the insulation. We report details of the specimens’ preparation, test procedures and test results.
2010 8th International Pipeline Conference, Volume 4, 2010
ABSTRACT Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) dia... more ABSTRACT Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) diameter and 0.75-inch (19-mm) wall thickness, has been initiated in support of strain-based design using high strength steel for oil and gas pipeline applications. The CWP tests are being used to optimize and validate welding procedures and to determine the defect tolerance within the girth welds. A traditional pre-requisite for fracture mechanics testing is a final extension of a crack via fatigue pre-cracking to produce a representative flaw. A method of fatigue pre-cracking CWP specimens for final notch preparation in bending was developed to meet ASTM guidelines for fracture mechanics testing. Fatigue pre-cracking for the present specimen geometry was possible in bending due to lower requisite force capacity equipment which allowed for greater cyclic loading frequencies. In order to achieve sufficient stress levels for fatigue crack growth in the curved plate, a stress field analysis was performed to optimize the loading support configuration in four-point bending. In addition to the stress field analysis, a 3-D finite element model of the CWP specimen was generated to analyze the notched CWP specimen in four-point bending. Finite element analysis (FEA) results and experimental data were used to confirm the hypothesis that, under the proposed loading arrangement, the closed-form solutions for stress-intensity (K) of flat plates in bending can be used to approximate the K for CWP specimens in bending. Validation of a solution for stress-intensity factor subsequently allowed the determination of force amplitude levels for fatigue crack growth. Force and crack mouth opening displacement (CMOD) data were analyzed to correlate compliance with crack length measurements. From experimental results, a method was developed that enable the repeatable and well characterized extension of surface flaws by fatigue pre-cracking in curved wide plate specimens in bending.
In Part I of this program, Al-Li alloys 8090-T3 and 2090-T81 and Al alloy 2219 (tempers T851, T37... more In Part I of this program, Al-Li alloys 8090-T3 and 2090-T81 and Al alloy 2219 (tempers T851, T37) were tested for compatibility with liquid oxygen using pressurized mechanical-impact apparatuses at two NASA laboratories, Marshall Space Flight Center (MSFC) and White Sands Test Facility (WSTF). Specimens and data from tests at Santa Susana Field Laboratory (SSFL), Rocketdyne, on alloy 2090-T81 were supplied by ALCOA. Pressurized mechanical- impact data on alloy WL049-T351 were produced by WSTF. In addition, WSTF conducted open-cup mechanical-impact and promoted-combustion tests on all alloys. Reactions occurred in some specimens of all alloys during pressurized mechanical-impact tests at MSFC. There were no reactions during similar tests at WSTF and SSFL. The reactions at MSFC are not attributed to specimen contamination. This interim report analyzes the ignitions found in the MSFG pressurized mechanical-impact tests, compares the results and test methodologies of both MSFC and WSTF...
The report details a large mechanical test program undertaken by the NIST Materials Reliability D... more The report details a large mechanical test program undertaken by the NIST Materials Reliability Division. These tests were intended to validate the full scale structural behavior of the composite support struts in a thermal and mechanical environment identical to actual service conditions. Two types of tests were performed: ultimate compressive strength and fatigue. Thermal conditions for the tests ranged from isothermal, room temperature tests to an imposed thermal gradient of cryogenic-to-room temperatures. The development of the unique facility necessary for the large scale cryogenic tests is detailed in the report.
Tensile and plane-strain fracture toughness properties were obtained at cryogenic temperatures to... more Tensile and plane-strain fracture toughness properties were obtained at cryogenic temperatures to compare the Al-Li alloys 8090, 2090, and WL049 and alloy 2219 in various tempers and specimen orientations. The strongest alloy at very low temperatures is WL049-T851, which is about 10% stronger than 2090-T81. Both alloys are considerably stronger than 2219-T87. Alloy 2090-T81 is tougher in the in-plane orientations (about 50%) than WL049-T851 at low temperatures; the higher in-plane toughness is attributed to the presence of less constituent particles and the tendency to crack out-of-plane or delaminate at low temperatures. This delamination tends to divide the moving crack, thus separating it into smaller regions where plan stress (rather than plane strain) conditions are conducive to increased toughness. Thus, a dichotomy: reduced toughness in the through-thickness or out-of-plane orientations leads to increased toughness in the in-plane orientations. In service, a leak in the tank ...
A test for evaluation of resistance to ductile fracture [crack tip opening angle (CTOA)] was foun... more A test for evaluation of resistance to ductile fracture [crack tip opening angle (CTOA)] was found to reveal changes in crack extension through the heat-affected zone (HAZ) and weld interface in X100 pipeline steels. This test provides a long ligament for crack extension data not available in Charpy or drop-weight tear specimens, and is much less expensive than the full-scale burst tests. The ductile-fracture resistance of girth welds, perpendicular to the growing crack, and seam welds and their HAZs, parallel with the crack, were evaluated. Analysis of the data reveals some general differences, such as changes in CTOA and crack extension rate as the crack Moved through the base metal, HAZ, and girth weld material. The values for CTOA were observed to increase and the crack extension rate decreased as the crack moved through the weld and approached the weld interface. The plastic deformation appears to be strongly influenced by the properties and geometry of the narrow HAZ, the weld...
2008 7th International Pipeline Conference, Volume 3, 2008
When a crack initiates and propagates in a pressurized pipe, the only thing that might stop this ... more When a crack initiates and propagates in a pressurized pipe, the only thing that might stop this high-velocity event is the release of internal pressure (decompression), resulting in a deceleration in the crack-propagation rate. This deceleration can be achieved through the use of crack ...
2010 8th International Pipeline Conference, Volume 2, 2010
ABSTRACT Two types of specimen for crack tip opening angle (CTOA) measurement have been investiga... more ABSTRACT Two types of specimen for crack tip opening angle (CTOA) measurement have been investigated for pipeline applications, i.e., the modified double cantilever beam (MDCB) (at NIST) and the drop-weight tear test (DWTT) specimen (at CANMET). Results of effects of specimen types, thicknesses and loading rates on CTOA are summarized and discussed. The main observations include: (i) For both MDCB and DWTT specimens tested at quasi-static loading rate, crack front tunnelling (i.e., with a deep triangular crack-tip shape) was present in high-strength steels; (ii) For DWTT specimens, CTOA values measured optically at the surface were significantly higher than those from the simplified single-specimen method (S-SSM) and those measured at mid-thickness [on sections cut using electric discharge machining (EDM)]; and (iii) CTOA values from surface measurement of MDCB specimens were comparable to those derived from S-SSM of DWTT specimens, but the surface values of DWTT were higher than those of MDCB specimens.
2008 7th International Pipeline Conference, Volume 3, 2008
ABSTRACT The toughness and plasticity of steel generally decreases with increasing testing rate. ... more ABSTRACT The toughness and plasticity of steel generally decreases with increasing testing rate. The crack tip opening angle (CTOA) was measured on two types of commercial pipeline steels API-X65 and API-X100, at a range of displacement rates to characterize rate effects. The testing was conducted at quasi-static and dynamic rates. The crosshead displacements in our test matrix ranged from 0.002 mm/s in the quasi-static mode to approximately 8000 mm/s in the dynamic mode. The quasi-static tests were conducted in a servo-hydraulic uniaxial test machine using Modified Double Cantilever Beam (MDCB) specimens. The dynamic experiments were made on a similar servo-hydraulic uniaxial test machine using the same type of specimen and with the addition of a disc spring setup for the fastest rate. The results of these tests indicate that the rate effect has negligible influence on the CTOA values measured for these materials for the reported rates. The CTOA values measured for the two materials show a small but convincing difference. The resistance to fracture was found to be higher for the X65 steel, as indicated by a higher CTOA and lower crack growth velocity. This paper presents results on the influence of displacement rates from quasi-static to dynamic for the X65 and X100 grade pipeline steels, and discusses a method for optimizing the reduction of the CTOA data.
A system is described based on electromagnetic acoustic transducers (EMATs) as an approach to aut... more A system is described based on electromagnetic acoustic transducers (EMATs) as an approach to automated nondestructive evaluation of thick weldments. Applications include a new type of ultrasonic inspection system for thick, butt welds used in ship construction. A minicomputer controlled transducer positioned and acquired the digitized ultrasonic waveforms for synthetic aperture processing. The synthetic aperture technique further improved signal quality and yielded flaw localization through the weld thickness. Details include the design of the transducers and electronics, as well as the mechanical positioner, signal processing algorithms, and complete computer program listings.
ABSTRACT The assessment of hydrogen content in pipeline steel is an essential requirement to moni... more ABSTRACT The assessment of hydrogen content in pipeline steel is an essential requirement to monitor loss of pipe integrity with time and to prevent failures. The use of pipeline steels of increasing strength significantly reduces the threshold hydrogen concentration for hydrogen cracking. Cathodic protection and corrosion processes both contribute to accumulation of hydrogen as a function of time, which may eventually meet the cracking criteria. New and unique methodologies based on electronic property measurements offer the pipeline industry advanced non-destructive tools to provide quantified in-situ hydrogen content measurements in real-time. The use of low frequency impedance measurements as a non-contact sensor has been demonstrated for real-time determination of hydrogen content in coated pipeline steel specimens in the laboratory. Scale-up to field measurements is in progress, and the development and use of a field sensor are discussed.
ABSTRACT A measurement system has been developed to investigate the technology required for high-... more ABSTRACT A measurement system has been developed to investigate the technology required for high-power gas-coupled ultrasonics and the phenomenology of finite-amplitude of ultrasonic waves in gases at high frequencies (>10 MHz) and pressures up to 10 MPa (100 bar). Results of measurements of compression wave absorption and velocity in argon between 10 and 25 MHz, with various combinations of pressure, temperature and power level are presented. For small-amplitude waves, the resulting data are in good agreement with those calculated using ideal gas equations and fundamental thermophysical gas constants. At higher power levels, nonlinear phenomena are observed
An insulation system for ITER Central Solenoid must have sufficiently high electrical and structu... more An insulation system for ITER Central Solenoid must have sufficiently high electrical and structural strength. Design efforts to bring stresses in the turn and layer insulation within allowables failed. It turned out to be impossible to eliminate high local tensile stresses in the winding pack. When high local stresses can not be designed out, the qualification procedure requires verification of the acceptable structural and electrical strength by testing. We built two 4×4 arrays of the conductor jacket with two options of the CS insulation and subjected the arrays to 1.2 million compressive cycles at 60 MPa and at 76 K. Such conditions simulated stresses in the CS insulation. We performed voltage withstand tests and after end of cycling we measured the breakdown voltages between in the arrays. After that we dissectioned the arrays and studied micro cracks in the insulation. We report details of the specimens’ preparation, test procedures and test results.
2010 8th International Pipeline Conference, Volume 4, 2010
ABSTRACT Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) dia... more ABSTRACT Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) diameter and 0.75-inch (19-mm) wall thickness, has been initiated in support of strain-based design using high strength steel for oil and gas pipeline applications. The CWP tests are being used to optimize and validate welding procedures and to determine the defect tolerance within the girth welds. A traditional pre-requisite for fracture mechanics testing is a final extension of a crack via fatigue pre-cracking to produce a representative flaw. A method of fatigue pre-cracking CWP specimens for final notch preparation in bending was developed to meet ASTM guidelines for fracture mechanics testing. Fatigue pre-cracking for the present specimen geometry was possible in bending due to lower requisite force capacity equipment which allowed for greater cyclic loading frequencies. In order to achieve sufficient stress levels for fatigue crack growth in the curved plate, a stress field analysis was performed to optimize the loading support configuration in four-point bending. In addition to the stress field analysis, a 3-D finite element model of the CWP specimen was generated to analyze the notched CWP specimen in four-point bending. Finite element analysis (FEA) results and experimental data were used to confirm the hypothesis that, under the proposed loading arrangement, the closed-form solutions for stress-intensity (K) of flat plates in bending can be used to approximate the K for CWP specimens in bending. Validation of a solution for stress-intensity factor subsequently allowed the determination of force amplitude levels for fatigue crack growth. Force and crack mouth opening displacement (CMOD) data were analyzed to correlate compliance with crack length measurements. From experimental results, a method was developed that enable the repeatable and well characterized extension of surface flaws by fatigue pre-cracking in curved wide plate specimens in bending.
In Part I of this program, Al-Li alloys 8090-T3 and 2090-T81 and Al alloy 2219 (tempers T851, T37... more In Part I of this program, Al-Li alloys 8090-T3 and 2090-T81 and Al alloy 2219 (tempers T851, T37) were tested for compatibility with liquid oxygen using pressurized mechanical-impact apparatuses at two NASA laboratories, Marshall Space Flight Center (MSFC) and White Sands Test Facility (WSTF). Specimens and data from tests at Santa Susana Field Laboratory (SSFL), Rocketdyne, on alloy 2090-T81 were supplied by ALCOA. Pressurized mechanical- impact data on alloy WL049-T351 were produced by WSTF. In addition, WSTF conducted open-cup mechanical-impact and promoted-combustion tests on all alloys. Reactions occurred in some specimens of all alloys during pressurized mechanical-impact tests at MSFC. There were no reactions during similar tests at WSTF and SSFL. The reactions at MSFC are not attributed to specimen contamination. This interim report analyzes the ignitions found in the MSFG pressurized mechanical-impact tests, compares the results and test methodologies of both MSFC and WSTF...
The report details a large mechanical test program undertaken by the NIST Materials Reliability D... more The report details a large mechanical test program undertaken by the NIST Materials Reliability Division. These tests were intended to validate the full scale structural behavior of the composite support struts in a thermal and mechanical environment identical to actual service conditions. Two types of tests were performed: ultimate compressive strength and fatigue. Thermal conditions for the tests ranged from isothermal, room temperature tests to an imposed thermal gradient of cryogenic-to-room temperatures. The development of the unique facility necessary for the large scale cryogenic tests is detailed in the report.
Tensile and plane-strain fracture toughness properties were obtained at cryogenic temperatures to... more Tensile and plane-strain fracture toughness properties were obtained at cryogenic temperatures to compare the Al-Li alloys 8090, 2090, and WL049 and alloy 2219 in various tempers and specimen orientations. The strongest alloy at very low temperatures is WL049-T851, which is about 10% stronger than 2090-T81. Both alloys are considerably stronger than 2219-T87. Alloy 2090-T81 is tougher in the in-plane orientations (about 50%) than WL049-T851 at low temperatures; the higher in-plane toughness is attributed to the presence of less constituent particles and the tendency to crack out-of-plane or delaminate at low temperatures. This delamination tends to divide the moving crack, thus separating it into smaller regions where plan stress (rather than plane strain) conditions are conducive to increased toughness. Thus, a dichotomy: reduced toughness in the through-thickness or out-of-plane orientations leads to increased toughness in the in-plane orientations. In service, a leak in the tank ...
A test for evaluation of resistance to ductile fracture [crack tip opening angle (CTOA)] was foun... more A test for evaluation of resistance to ductile fracture [crack tip opening angle (CTOA)] was found to reveal changes in crack extension through the heat-affected zone (HAZ) and weld interface in X100 pipeline steels. This test provides a long ligament for crack extension data not available in Charpy or drop-weight tear specimens, and is much less expensive than the full-scale burst tests. The ductile-fracture resistance of girth welds, perpendicular to the growing crack, and seam welds and their HAZs, parallel with the crack, were evaluated. Analysis of the data reveals some general differences, such as changes in CTOA and crack extension rate as the crack Moved through the base metal, HAZ, and girth weld material. The values for CTOA were observed to increase and the crack extension rate decreased as the crack moved through the weld and approached the weld interface. The plastic deformation appears to be strongly influenced by the properties and geometry of the narrow HAZ, the weld...
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